This invention relates to techniques for converting alcohol feedstocks, such as crude methanol or the like, to lower ether products, eg-methyl tertiary-alkyl ethers. This invention also provides a technique for converting methanol to lower olefins. In particular, it provides a continuous process for producing an intermediate olefinic product rich in C.sub.2 -C.sub.5 alkenes. In view of the availability and low cost of synthetic methanol (MeOH), primary emphasis is placed on this feedstock material in following description of the methanol-to-olefin (MTO) process.
In its broader aspects, this invention relates to an integrated system for converting crude methanol to valuable products by etherifying lower branched olefins, such as C.sub.4 -C.sub.5 isoolefins. It is known that isobutylene may be reacted with methanol over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) and isoamylenes may be reacted with methanol over an acidic catalyst to produce tertiary-amyl methyl ether (TAME). The etherification catalyst employed is preferably an ion exchange resin in the hydrogen form. Substantially any acidic catalyst may be employed with varying degrees of success. That is, acidic solid catalysts may be used; such as, sulfonic resins, phosphoric acid modified kieselguhr, silica alumina and acid zeolites. Those ethers having the formula CH.sub.3 -O-R, where R is an isoalkyl radical, are particularly useful as octane improvers for liquid fuels, especially gasoline.
Increasing demand for high octane gasolines blended with lower aliphatic alkyl ethers as octane boosters and supplementary fuels has created a significant demand for tert-alkyl ethers, especially the C.sub.5 to C.sub.7 methyl alkyl ethers, such as methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME). Methanol may be readily obtained from coal by gasification to synthesis gas and conversion of the synthesis gas to methanol by well-established industrial processes. As an alternative, the methanol may be obtained from natural gas by other conventional processes, such as steam reforming or partial oxidation to make the intermediate syngas. Crude methanol from such processes usually contains a significant amount of water, usually in the range of 4 to 20 wt%; however, the present invention is useful for removing water in lesser amounts or greater.
Proceses for converting lower oxygenates such as methanol to hydrocarbons are known (eg-methanol-to -olefins -MTO), and have become of great interest in recent times because they offer an attractive way of producing liquid hydrocarbon fuels, especially gasoline, from sources which are not of liquid petroleum origin. In particular, they provide a way by which methanol can be converted to a major amount of C.sub.2 -C.sub.5 olefins and a minor amount of gasoline boiling range products in good yields.
It is main object of the present invention to provide a novel and economic technique for removing excess water from crude methanol feedstocks, including novel operating methods and equipment for treating these oxygenate feedstocks prior to conversion to olefins and etherification.